TITLE: GCN CIRCULAR NUMBER: 15320 SUBJECT: GRB 130831A: VLT/FORS2 spectroscopic detection of a supernova DATE: 13/10/09 09:54:39 GMT FROM: Sylvio Klose at TLS Tautenburg S. Klose, A. Nicuesa Guelbenzu (both TLS Tautenburg), T. Kruehler (ESO), J. Greiner, D. A. Kann, A. Rau, V. Sudilovsky (all MPE Garching), F. Olivares E. (UNAB, MCSS, Chile), and S. Schulze (PUC, MCSS, Chile), on behalf of a larger collaboration report: We observed the optical transient following GRB 130831A (e.g., Hagen et al. 2013, GCN 15139; Guidorzi et al. 2013, GCN 15140; Xu et al. 2013, GCN 15142; Yoshii et al. 2013, GCN 15143) with VLT/FORS2 equipped with the 300V grism on Sep 29 and Sep 30, 2013, between 28.5 and 29.5 days after the burst under excellent sky conditions with mean seeing around 0.6". The total exposure time of the spectrum was 1.53 hr and covers the spectral range between approximately 440 and 920 nm. In the combined spectrum, we detect the optical emission over the full spectral range. The spectrum peaks at about 800 nm and shows broad absorption features, very much reminiscent of the spectrum of, e.g., GRB 031203 / SN 2003lw (z=0.1055; Malesani et al. 2004, ApJ 609, L5), and the recent GRB 120714B / SN 2012eb (z=0.40; Klose et al. 2012, GCN 13613), GRB 130215A / SN 2013ez (z=0.597; de Ugarte Postigo et al., GCN 14303), GRB 130427A / SN 2013cq (z=0.34; Xu et al. 2013, ApJ 776, 98), and GRB 130702 / SN 2013dx (z=0.145; Schulze et al. 2013, GCN 14994), all obtained around SN maximum light. We conclude that we have spectroscopically discovered the appearence of a broad-line SN following GRB 130831A at z=0.4791 (Cucchiara et al. 2013, GCN 15144), confirming the conclusion of Pozanenko et al. (GCN 15237) based on the optical light curve. [GCN OPS NOTE(12oct13): Per author's request, VS was added to the author list.]